Low-speed driving units utilizing an electric motor drive are well known in the prior art. The torque of such low-speed driving units, measured on the outlet shaft at rated speed, lies within the range of units per second as being of an order 100 Nm and has been characterized by a design feature based on a standard high-speed electric drive equipped with a gearbox. However, this part of the wheel proves to have the highest failure mode.
The operation of an advanced driving mechanism requires the development of a contactless electric motor without a gearbox to be maintenance free for the whole lifetime.
In Czech patent application 1480-97 A3 to Nicolas Wavre of Neuchatel, CH, Wavre—describes a synchronous motor with permanent magnets and fitting coils into a top land, where the coils are slid on the teeth with the axes oriented to the centre of the motor, which are connected by means of a magnetic yoke. However, in Wavre's disclosure, it is not possible to attain necessary weight and performance parameters.
Czech patent CZ 279 581 B6 (registrant the Institute of Thermo-technology of Academy of Sciences of the Czech Republic (stav termotechniky AVR), Prague, CZ) discloses a machine with a diameter greater than one meter by applying a principle of two rotors, one of them being equipped with magnets whereas the other has pairs of pole shoes with coils slid on. This device can be used for the purpose of a light motor with a large diameter. However, it is obvious that this arrangement cannot be used as a drive, due to an uncompensated flip-flop effect resulting in the generation of vibrations.
Czech patent CZ 291897 B6, dated 2001, discloses that conventional motors with gearboxes can be replaced by motors without gearboxes based on FeNdB magnets placed on the rotor and with stator coils wound on a continuous circular ring made from soft magnetic material, e.g., ferrite, where starting torque may be increased by increasing the radius of the position of the electric motor functional elements. This engineering design solution is technologically limited to diameters up to 300 mm. Because of the technological limitations regarding the manufacture of the ring made from soft magnetic material, this solution cannot be applied to the manufacture of the motors with the light design engineering features without a gearbox whose diameter exceeds 500 mm, with the width being a few centimeters and with the starting torque being of an order 100 Nm, and with a ratio of motor diameter to the motor thickness greater than 15.